When Hadingus was adolescent, fighting was all he ever thought about. Harthgrepa, Wagnhoftus's daughter, tried to make him discover love and made repeated attempts to seduce him. Finally, she sang him a song ending by:
Hadingus put forward that the big size of the giantess hindered this project. Harthgrepa replied that she had the ability to change size at will: "I become huge to fright the fierce, but small to lie with men" (ibid.). She then became Hadingus' lover.
When Hadingus decided to go back to his country, she came with him, dressed like a man. They spent one night in a house whose host had just died. Harthgrepa practised magic, making Hadingus put a wood stick carved with spells under the corpse's tongue, thus compelling him to speak. He cursed them and predicted their future, especially Harthgrepa's death.
Another night, while they were sleeping in a wood, a huge hand entered their shelter. Harthgrepa then got bigger and, holding firmly the hand, pulled it so that Hadingus could chop it off.
A short time after, she was killed, torn apart by giants.
In The Saga of Hadingus, Georges Dumézil tries to demonstrate that the legend of Hadingus shows many similarities with myths concerning the god Njörðr, and more generally that Hadingus shares many features with the Vanir. Some of his arguments have to do with Hadingus' relationship with Harthgrepa.
Before their integration into the Æsir, the Vanir used to have incestuous relationships (Freyr and Freyja are for instance Njörðr and his sister's children). Hadingus' relationship with Harthgrepa is a quasi-incestuous one, all the more so that Harthgrepa insists on the fact that she was like a mother to him.
He also reminds that the Vanir used to practise this kind of magic known as seid. Even if Harthgrepa's magic (compelling a dead man to speak) does not come within the seid practices, both are described as shameful and liable to a punishment. In this respect, Harthgrepa's death can be compared to the Æsir's attempts to kill Gullveig.